1. Field of the Invention
This invention relates to a gamma-prime precipitation hardening nickel-base yttria particle-dispersion-strengthened superalloy.
More specifically, this invention relates to a gamma-prime precipitation hardening nickel-base yttria particle-dispersion-strengthened superalloy having excellent creep rupture strength.
The output or thermal efficiency of gas turbines used in jet engines or power plant facilities can be most effectively increased by elevating the temperature of combustion gases. For this purpose, blade materials having high creep rupture strength at high temperatures are required.
2. Description of the Prior Art
R. Irmann, Metallurgia, 49 (1952), page 125 describes a sintered aluminum product (SAP).
U.S. Pat. No. 2,972,529 discloses oxide dispersion-strengthened alloys such as TD Ni and TD Ni--Cr developed by utilizing the teaching of the above-cited literature reference. These alloys, however, have low creep rupture strength at intermediate temperatures region, and lack corrosion resistance.
U.S. Pat. No. 3,591,362 discloses an alloy producing method called the mechanical alloying method (MA method). This method enabled the production of oxide-dispersion strengthened superalloy with gamma-prime precipitates having fine oxide. The alloys disclosed in this patent, however, have a low grain aspect ratio (GAR), i.e. the ratio of the longitudinal length to its tansverse length, of a crystal grain and their creep rupture strength is not high.
U.S. Pat. No. 3,746,581 discloses that an alloy having a structure of a high GAR is obtained by the zone annealing method by which an extruded material produced under suitable extruding conditions is moved in a furnace having a temperature gradient.
U.S. Pat. Nos. 3,746,581 and 3,926,568 and Y. G. Kim and H. F. Merrick, NASA CR-159493, May 1979 describe alloys such as MA6000 produced by using the aforesaid MA method and zone annealing method. MA6000 alloy, one of the best alloys now on the market, is produced by mechanically mixing elemental powders, alloy powders and yttria so as to provide the desired alloy composition, extruding the mixture, and subjecting the extruded material to zone annealing heat-treatment. The resulting alloy is a gamma-prime phase precipitation hardening nickel base alloy dispersion-strengthened with fine particles of yttria. MA6000 alloy has a creep rupture strength at high temperatures of about 1,400 hours under creep conditions of 1,050.degree. C. and 16 kgf/mm.sup.2, which is higher than those of ordinary cast and single crystal alloys. But from the standpoint of the alloy design, it is not fully solid solution-strengthened, and particularly the balance between the contents of chromium and high-melting metals (W and Ta) is not satisfactory.
Japanese patent application No. 168761/1984 having the same inventorship as the present application, which was filed in Japan on Aug. 14, 1984, i.e. before the Convention priority date (Oct. 26, 1985) of the present application, and laid open to public inspection as Japanese Laid-Open Patent Publication No. 48550/1986 on Mar. 10, 1986, i.e. after the Convention priority date, describes a gamma-prime precipitation hardening nickel-base yttria particle-dispersion-strengthened superalloy having quite a different alloy composition from MA6000. This alloy is produced without zone annealing heat-treatment. Under creep conditions of 1,050.degree. C. and 16 kgf/mm.sup.2, this alloy has a creep rupture strength of about 3,500 hours, which is higher than that of MA6000, but is still not entirely satisfactory.